Hepatitis B Virus (HBV) is an enveloped DNA virus with an RNA intermediate. The core of the virus assembles as a protein shell around a viral mRNA and reverse transcriptase. In the cytoplasm, the encapsidated RNA is transcribed into DNA to yield the mature core. Worldwide, 360 million people suffer from chronic HBV infection. HBV causes liver dysfunction, cirrhosis, and hepatocellular carcinoma. It contributes to almost one million deaths each year. Though HBV can be prevented by vaccination, the vaccine is not therapeutic. Where available, the treatment of choice is monotherapy with a reverse transcriptase inhibitor. Unfortunately, this approach may select for resistant mutants. Ideally, an alternative target can be developed that will yield drugs suitable for combination therapy. We have proposed that HBV core assembly is such a molecular target. Based on theory, we suggest that the most effective approach will be to enhance assembly to tie up many core proteins in unproductive complexes. We have investigated several families of small molecules with assembly enhancing activity, in particular heteroaryldihydro- pyrimidines (HAPs). In the course of our studies we have examined about 150 different potential assembly effectors, developed high throughput screens, determined the HAP binding site crystallographically, and developed solution approaches to evaluate thermodynamic and kinetic responses of viruses to assembly effectors. We observed a strong correlation between assembly kinetics and antiviral effect in cultured cells. Now we propose to capitalize on these results by (i) searching for new assembly effectors, identifying alternative binding sites and lead compounds, and improving on the design of those in hand, (ii) defining the structural and physical chemical basis for assembly effector activity effect, (iii) investigating the ability of the core protein for developing resistance to assembly effectors, and (iv) examining how assembly effectors affect interactions between virus and host by examining how they alter the distribution of HBV cores in cells. These independent aims will move assembly effectors from the subject of purely academic investigation towards clinical application.